Active wear apparel and apparel designed to be worn in hot, humid environments are generally characterized as being well suited to be worn during times when one is likely to be perspiring. Optimally, the active wear garment should have some moisture management capability, while still remaining comfortable, providing freedom of movement and being easy to care for. One of the prime factors for garment comfort when perspiring heavily is how well the garment transfers moisture away from the skin. Additionally, for greater comfort after periods of heavy perspiration, the garment should optimally feel dry next to the skin or inner garments.
Garments made from cotton fabric and other natural material fabrics (such as linen, wool, etc.) are generally absorbent, and continue to feel comfortable under conditions of very light perspiration. This is because the fabric absorbs the relatively small amount of moisture produced at these times, keeping the wearer feeling dry. However, under conditions of heavier perspiration, these fabrics feel wet, heavy and clingy, restricting movement and becoming uncomfortable to wear. Additionally, once these fabrics become wet, they take a long time to dry, and continue to feel damp and uncomfortable until they have fully dried. This dampness can have other undesirable effects on the wearer as well. For example, wet fabrics are known to have increased friction against skin. This dramatically increases the chafing and even blistering resulting from movement, commonly suffered during athletic activity. Also, a damp fabric tends to chill the wearer, once physical activity is stopped, through excessive evaporative cooling. This is most prominent when the dampness is in direct contact with the skin. Comfort is particularly compromised with wool garments, which become much more irritating to the skin when damp.
Fabrics made from untreated polyester, nylon and other synthetic materials do not readily absorb moisture, due to being hydrophobic. As a result, when untreated synthetic fabrics are worn under conditions of even moderate perspiration, moisture tends to build up on the skin, because the fabric does not absorb moisture. Thus, when wearing untreated garments made of synthetic fibers, water tends to bead up and become trapped on the inner surface of the garment, resulting in an extremely uncomfortable garment.
A variety of methods have been used to improve the moisture transfer characteristics of untreated fabrics; three are outlined here. One common method is to apply a hydrophilic finish to a hydrophobic fabric made from synthetic fibers, rendering it a wicking fabric. A second method of improving moisture transfer is to use various fabric construction techniques to create fabrics that are more hydrophobic on one surface and more hydrophilic on the other surface, leading to moisture transfer from the hydrophobic side to the hydrophilic side. A third method has been developed for cotton by treating one side of the fabric with a discontinuous hydrophobic coating, leaving untreated areas as “wicking channels” in the fabric. These three methods are described below:
In the first method, as mentioned above, a hydrophilic finish is applied durably to a synthetic fiber fabric. For example, see U.S. Pat. Nos. 6,855,772 and 6,544,594. These fabrics quickly transfer and spread moisture, increasing the surface area of the moisture to enhance evaporation. Since the underlying fibers are hydrophobic, the fibers themselves do not absorb moisture, unlike cotton or wool fibers. Because these fabrics do not absorb moisture into the fibers themselves, the moisture resides primarily in the capillaries between fibers and yarns. This enhances lateral wicking, which may lead to a greater surface area of the moisture and thus faster drying. However, the moisture still resides throughout the thickness of the fabric. This means that the inner surface (touching the skin) can remain wet and clingy. In addition, when compared to natural fiber fabrics, synthetic fiber fabrics are generally known to have other undesirable properties, such as pilling, static cling, odor retention, and an “unnatural” feel. This type of hydrophilic-treatment is designed primarily for synthetic fabrics.
In the second method, various kinds of fabric construction techniques have also been used to create fabrics that transfer moisture form one side of the fabric to the other. One such fabric construction is described in U.S. Patent Publication No. 2003/0181118, which describes generally a fabric made from two different types of yarn, where one yarn is more hydrophilic and the other is more hydrophobic. These yarns are woven or knitted in such a way that the hydrophobic yarns are predominantly on one side of the fabric and the hydrophilic yarns are primarily on the other side of the fabric. A portion of the hydrophilic yarns penetrates to the hydrophobic side, acting to channel liquid to the hydrophilic side. As a result, water is transferred from the hydrophobic side to the hydrophilic side, although some water remains on both sides, residing in the hydrophilic channels. A similar type of fabric construction is also described in U.S. Pat. No. 3,250,095 and U.S. Pat. No. 6,806,214. See also US 2006/0148356 and WO 2006/042375.
Another method of weaving or knitting more than one kind of yarn together is shown in U.S. Pat. No. 6,381,994. In this case, the two yarns are synthetic fiber yarns where one yarn has undergone a treatment that creates larger void sizes. These yarns are woven or knitted into a fabric in such a way that causes the treated fibers to be primarily on one side of the fabric and the untreated fibers to be primarily on the other side of the fabric. Moisture transport across the fabric is driven by the difference in void sizes between the types of yarns.
Another example of fabric construction techniques consists of a fabric construction wherein the final fabric is made from layers of two different hydrophilic fabrics, as is described in U.S. Pat. No. 6,432,504. One layer (the interior or “skin” side of a garment) is made from coarser fibers, while the second layer is made from finer fibers. Both layers will absorb and wick moisture, but the outer layer made from finer fiber has greater moisture absorbency, due to the smaller fiber size and thus a stronger capillary wicking force. This difference in absorbency drives moisture transfer from the less absorbent (coarser fiber) layer to the more absorbent (finer fiber) layer. This type of construction is commonly referred to as “denier gradient.”
A more complex fabric construction is described in U.S. Pat. Publn. 2003/0182922. This patent describes two fabrics that enhance moisture transfer. The fabric construction depends on the use of composite yam that has an inner core of hydrophilic fibers surrounded by an outer sheath of hydrophobic fibers. The first fabric described is made from the composite yarn alone. The second fabric is comprised of two layers of fabric components bound together. The inside fabric component is made from only hydrophobic fibers. The outside fabric component is made from the above-described composite yarn. These two fabric components are joined together to form a fabric such that the fabric component made from only hydrophobic fibers is on the inner face of the fabric and the fabric component made from composite yarn (hydrophilic) is on the outer face of the fabric. Moisture transfer through this two-layered fabric is driven by the difference in hydrophilicity between the inner (hydrophobic) layer and the outer (hydrophilic) layer, but generally requires some extent of wicking channels in the form of hydrophilic yarns or fiber bundles that traverse from outside to the inner side.
All of these fabric construction techniques described above involve somewhat complicated weave or knit constructions combined with specialty yarns, thus limiting their applicability. In addition, such constructions are generally not effective at leaving the inside surface of the fabric (touching the skin) dry. In practice, these fabrics will move a portion of liquid moisture from the inside to the outside, but a significant portion will remain on the inside, thus still feeling wet.
In the third method, a method of treating cellulosic fabrics to form a discontinuous hydrophobic coating is described in U.S. Pat. No. 7,008,887. In this case, the cellulosic fabric (which is naturally hydrophilic) is treated on the inside with a hydrophobic finish (such as a fluoropolymer, silicone, or waxy polymer). The finish is applied in a discontinuous pattern, such that “wicking channels” (i.e. untreated regions of fabric) are formed. Moisture is absorbed into the untreated wicking channel regions and then wicks to the other areas of the garment to enhance evaporation. Other coating methods are also described, such as continuous hydrophobic coatings coupled with the creation of wicking windows or channels, e.g., by using needle punching to push through cellulosic fibers that are capable of wicking liquid from the inside to the outside of the fabric. However, wicking channels will remain wet and in contact with the skin, which is uncomfortable to the wearer. In addition, the method described in this patent is limited to cellulosic substrates.
In all of the aforementioned examples, attempts have been made using mechanical approaches (such as by combining materials or forming wicking channels) to enhance the transfer of moisture from one side of a fabric to another. These (and other) mechanical approaches often use complicated materials and fabric construction techniques, and are thus limited in the types of fabrics for which they are useful. The fabrics of these examples are either difficult or expensive to manufacture, require specialty fibers, and/or do not effectively leave the inner surface of the fabric dry under moderate to heavy perspiration situations.
There thus exists a need for alternative methods and compositions for imparting moisture transfer capability to a fabric and for fabrics treated by such methods and with such compositions.